1. Field of the Invention
The present invention is generally related to a method for avoiding injury to the operator of a machine tool and, more particularly, to a method which detects a preselected color representing a human body part within one or more zones proximate a potential cause of injury.
2. Background of the Invention
Those skilled in the art of the design, manufacture, and use of machine tools are aware of many different techniques used to reduce the likelihood of injury to the operator of the machine tool. These techniques include many different types of sensors, shields, and barriers, which are intended to prevent various body parts from moving into contact with injury causing components of the machine tool.
U.S. Pat. No. 4,249,074, which issued to Zettler et al. on Feb. 3, 1981, describes an intrusion detector for a press brake. The system is intended for safeguarding an operator of an industrial machine such as a press brake. A light screen barrier comprises sequentially pulsed beams which are spaced far enough apart to permit penetration by a work piece without obstructing more than one beam whereas penetration by the operator's hand will obstruct at least two adjacent successfully pulsed beams.
U.S. Pat. No. 5,140,649, which issued to Kageyama on Aug. 18, 1992, describes a gradation correcting apparatus for correcting luminance signal in accordance with detected color signal. It uses histogram memories in the television image receiving machine. When color picture signals have been inputted, the picture portion having the particular color component is detected so as to digitally affect the gradation correcting operation in accordance with the color component.
U.S. Pat. No. 5,649,021, which issued to Matey et al. on Jul. 15, 1997, describes a method and system for object detection for instrument control. The device may be a cutting tool for use in surgery, or other type of device applied to transform a specific object located in a defined area. The apparatus comprises a marker having a predetermined color. The marker is applied to the specific device or tool to form a marked device. An imager generates video signals representing a to color image of the defined area. A color detector processes the imager signal to detect a range of colors in the image represented by the imager signals. The range of colors includes the predetermined color. The color detector provides an output signal representing instances of signals in the detected color range.
U.S. Pat. No. 5,821,993, which issued to Robinson on Oct. 13, 1998, describes a method and system for automatically calibrating a color camera in a machine vision system. A pair of calibration algorithms are provided for calibrating a color camera in a machine vision system. The first and most general form of the calibration algorithm requires that a calibration target be shown to a well adjusted machine vision system. The calibration target contains samples of red, green and blue. A gray level histogram is taken of each of the resulting red, green and blue images and is used to generate corresponding standard cumulative probability functions.
U.S. Pat. No. 6,016,161, which issued to Robinson on Jan. 18, 2000, describes a method and system for automatically calibrating a color based machine vision system. The system includes a color camera, a frame grabber and an illumination source wherein subsequently acquired images are processed on a pixel-by-pixel basis. After the frame grabber offsets are measured to obtain initial or offset calibration data, the camera is pointed at a target monotone patch of known reflectance such as pure white and the camera outputs for red, green and blue are determined while observing the monotone patch to obtain spatial calibration data.
U.S. Pat. No. 6,122,014, which issued to Panusopone et al. on Sep. 19, 2000, describes a modified chroma keyed technique for simple shape coding for digital video. An optimized binary keying threshold is provided for switching between a first image region (such as a background region) and a second image region (such as a foreground object) video picture.
U.S. Pat. No. 6,317,691, which issued to Narayan et al. on Nov. 13, 2001, describes a collision avoidance system utilizing machine vision taillight tracking. A vehicle-mounted sensing method and apparatus capable of monitoring the relative speed, distance, and closure rate between a sensor equipped host vehicle and a sensed target object is described. The sensor uses an electronic camera to passively collect information and to provide the information to a system that identifies objects of interest using visual clues such as color, shape, and symmetry.
U.S. Pat. No. 6,445,817, which issued to de la Torre-Bueno on Sep. 3, 2002, describes an apparatus for counting color transitions and areas in real time camera images. The system may include an input port for importing a stream of pixels in a frame. The pixels in the frame with particular colors may be counted and stored by associated counters. The frame may be loaded simultaneously into four frame memories. Each frame memory may be read out in a different pattern, for example, horizontally, vertically, diagonally, and cross-diagonally.
U.S. Pat. No. 6,462,811, which issued to Turner et al. on Oct. 8, 2002, describes an automatic circular saw tooth inspection system and method. First and second video cameras mounted on the apparatus relative to the inspection zone provide output signals representative of the images of the first and second surfaces, respectively. A computer responsive to the output signals generated by the first and second video cameras analyzes the output signals and calculates selected attributes of the surfaces presented for inspection.
U.S. Pat. No. 6,469,734, which issued to Nichani et al. on Oct. 22, 2002, describes a video safety detector with shadow elimination. The machine vision safety solution digitally filters a configurable number of time sequenced images of a viewed area to create a filtered image. A textured background is used as a static target and viewed under ambient light, or alternatively a texture is observed under infrared light.
European Patent Specification EP 1 442 834, which was filed on Jan. 30, 2004 by Minalga et al., describes a machine safety protection system. It relates to a safety system for a machine, particularly for a tool having a moving blade. The concept also relates to a system to detect when a human is in close proximity to a dangerous area of the tool.
U.S. Pat. No. 6,578,712, which issued to Lawandy et al. on Jun. 17, 2003, describes methods and apparatus employing multi-spectral imaging for the remote identification and sorting of objects. The system can be used to mark and code textiles, linens, garments, documents and packages for high speed machine identification and sorting. Specific uses include garment and textile rental operations, laundry operations, and the postal and mail sorting of documents and packages.
U.S. Pat. No. 6,813,983, which issued to Gass et al. on Nov. 9, 2004, describes a power saw with improved safety system. A miter saw having a base and an arm that pivots toward the base is disclosed. A blade is supported by the arm, and is designed to cut work pieces resting on the base when the arm and blade pivot downward. The saw includes a detection system configured to detect one or more dangerous conditions between a person and the blade, such as when a person accidentally touches the spinning blade, and the saw includes a reaction system to urge the arm and blade away from the base when the dangerous condition is detected.
U.S. Pat. No. 6,829,371, which issued to Nichani et al. on Dec. 7, 2004, describes an auto setup of a video safety curtain system. Objects within view in a training phase are detected and compared to objects detected in a run time phase. Each new image is then compared to the previously created model and a pixel oriented difference image is calculated. The difference image is then processed for segmentation features attributable to an intruder object. Alarm conditions are determined from threshold parameters related to location of the intruder objects.
U.S. Pat. No. 6,900,728, which issued to Metzger on May 31, 2005, describes a system to detect user entry into a defined danger zone. It includes a non-conducting member defining an opening therein for receiving a saw blade. The non-conducting member may comprise, for example, an insert received by an opening in the work surface or table of a table saw, scroll saw, band saw, miter saw, etc. Alternatively, it may comprise the blade guard of a radial arm saw or miter saw. A conductor sensor is situated on the non-conducting member adjacent the opening to define a danger zone near the saw blade.
U.S. Pat. No. 6,922,153, which issued to Pierga et al. on Jul. 26, 2005, describes a safety detection and protection system for power tools. The system for detecting a dangerous condition for an operator using a power tool of the type which has an exposed blade relative to a work surface and a protection system for minimizing, if not eliminating, the possibility of a user being injured by contacting the blade is described. In one preferred embodiment, a proximity detection system is capable of detecting the presence of a user near the blade of a table saw and a protection system that can either retract the blade below the work surface of the table saw or terminate the drive torque to the blade which can result in a rapid stopping of the saw blade by a work piece that is being cut.
U.S. Pat. No. 6,959,631, which issued to Sako on Nov. 1, 2005, describes a power tool. It may include a table on which a work piece is positioned. A portion of a circular blade protrudes above the table. A circular blade may be driven by a motor. The motor may be controlled by a control device. The work piece is cut by means of an operator sending the work piece positioned on an upper face of the table in the direction of the circular blade while the circular blade is being driven by the motor. The power tool may include a first radar device and a second radar device for monitoring a predetermined area in the vicinity of the circular blade.
U.S. Pat. No. 7,049,967, which issued to Grasselli et al. on May 23, 2006, describes a safety system for machine tools. It comprises a pair of gloves to be worn by the operator and provided with an outer surface of dielectric material and an electrically conductive inner surface. An alarm signal generator connected to the conductive inner surface and a processor unit connected to the metal machine members and to at least one tool via a safety circuit arranged to sense the alarm signal when the operator cuts one of the gloves on coming into contact with one of the mechanical members of the machine are provided.
U.S. Pat. No. 7,084,779, which issued to Uneyama on Aug. 1, 2006, describes a power tool. The power tool is equipped with a radar for transmitting radio waves towards an area in a vicinity of a rotating tool and for receiving reflected radio waves reflected from a radio wave reflector existing within the area. From the reflected radio waves received by the radar, a distance between the radio wave reflector and the radar, and a speed of change of that distance are calculated.
U.S. Pat. No. 7,167,575, which issued to Nichani et al. on Jan. 23, 2007, describes a video safety detector with projected pattern. A known structured lighting texture pattern is projected upon a target area. A model image of the pattern on an empty target field is stored during an initial training step. The machine vision safety solution digitally interprets a camera image of the light reflected by the objects in the target area to detect and characterize a pattern in the image.
U.S. Pat. No. 7,311,276, which issued to Matlin et al. on Dec. 25, 2007, describes a shredder with a proximity sensing system. It includes a proximity sensing system to sense the presence of a person, animal, or object near cutting elements of the shredder.
U.S. Pat. No. 7,421,315, which issued to Gass et al. on Sep. 2, 2008, describes a detection system for power equipment. A detection subsystem is adapted to detect contact between a person and a specified portion of a machine and to distinguish that contact from contact with other materials. The detection subsystem imparts an electrical signal to a specified portion of the machine, and distinguishes that contact based on a predetermined frequency response of the electrical signal. A reaction subsystem then causes a predetermined action to take place. The machine may be a power saw designed to minimize injury in the event a person accidently contacts the blade.
An article on the Internet, at http://www.cybercollege.com/tvp015.htm, provides a helpful description of how color television systems work. Beginning with a description of the electromagnetic spectrum and the effects of prisms and reflection on color, the article describes the subtractive and additive attributes of color and the effects of combining primary colors to create secondary colors. In addition to discussing various attributes of contrast, the article describes three-chip video cameras and one-chip color cameras. In addition, the article provides a good basis for understanding how the eye visualizes color.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Certain techniques used to detect the presence of a body part, such as a hand or fingers, in a dangerous zone of a machine tool depend on the electrical characteristics of the human body. Others rely on a particular electrical characteristic of a glove worn by the operator of a machine tool. Those types of system require that the work piece and the body part have different electrical characteristics. This is not always possible. It would therefore be significantly beneficial if a system could be provided which is not adversely affected by the electrical characteristics of the work piece but which adequately detects and responds to the presence of a human body part in a danger zone of a machine tool.